This application relates primarily to pressure vessels. More specifically, this application relates to composite-overwrapped pressure vessels and all-composite pressure vessels. This application also relates to composite-overwrapped and all-composite tanks for storage of liquids and/or gases at relatively low pressures.
Pressure vessels and storage tanks find application in a wide assortment of industries. In certain industries, there is a particularly acute need for the pressure vessels to be of light weight. Some examples of these applications include the use of pressure vessels in self-contained breathing apparatus (SCBA) and gaseous fuel storage systems for automobiles, such as storage of compressed natural gas or hydrogen gas. In other applications, lightweight composite pressure vessels and storage tanks may be used on aircraft, launch vehicles, and spacecraft for chemical storage, transport, and/or mixing.
There are a number of different types of structures used for pressure vessels and storage tanks. Using a nomenclature common in the art, Type-I pressure vessels are fabricated of metal, Type-II pressure vessels are partially overwrapped metallic tanks, Type-III pressure vessels are composite-overwrapped structures that are lined with metal, and Type-IV pressure vessels are composite-overwrapped structures that are lined with a polymer. Of particular interest are “Type-V” pressure vessels, which are defined here as all-composite pressure vessels. Such pressure vessels may be especially suitable for lightweight applications like those identified above because they are projected to provide a weight reduction up to 25% when compared with conventional metal- or polymer-lined pressure vessels. Furthermore, Type-V pressure vessels have the potential of being manufactured more cheaply than Type-III and Type-IV pressure vessels due to the elimination of costly metal or polymer liners.
The composite outer layer on conventional composite-overwrapped pressure vessels with either metallic or polymeric liners is typically designed to safeguard against structural failure by rupture, while the liner is designed to contain the enclosed fluid. This effectively decouples the structural design of the pressure vessel from its fluid-containment requirements. There are three practical results of this decoupling of design requirements. First, the liners in Type-III and Type-IV pressure vessels are not mass-efficient in reacting the internal pressure load of the pressure vessel, which makes the liners a source of parasitic weight. Second, essentially the mode of failure in all lined pressure vessels (i.e., Type-III and Type-IV) when over-pressurized is catastrophic rupture of the structural shell—rather than leakage through the liner. However, for many applications, “leak-before-burst” failure performance, both under monotonic and cyclic pressurization, is desirable because it greatly reduces the likelihood of catastrophic failures of pressure vessels resulting in injury or death. Third, the liners in Type-III and Type-IV pressure vessels are, by definition, made of different materials than the composite outer shells. Hence, Type-III and Type-IV pressure vessels have performance limitations due to their use of dissimilar materials (e.g., limitations due to differential thermal-expansion, buckling and galvanic corrosion effects).
To address the first result above and in order to minimize the weight of composite pressure vessels, it is desirable to either eliminate the liner, or make the liner from a composite material that participates in reacting the internal pressure load in a mass efficient manner, while also preventing leakage of the contents.
To address the second result above and in order to design composite pressure vessels to exhibit a benign “leak-before-burst” failure mode, it is desirable to either eliminate the liner or design the liner such that it fails, predictably, before the composite outer shell fails.
To address the third result above and in order to eliminate performance limitations due to the use of dissimilar materials, it is desirable to either eliminate the liner or design the liner using a composite material that provides similar thermal, electrical and mechanical performance to the composite material used in the outer shell.
Past efforts to develop linerless composite pressure vessels and composite liners for composite-overwrapped pressure vessels have resulted in some successes. However, performance limitations of typical composite materials (i.e., lower-than-desired design operating strains) have typically resulted in higher-than-desired weights and/or un-predictable leakage and failure performance, in the case of linerless composite pressure vessels. Similarly, inadequate design, lack of precise failure prediction and improper material selection have resulted in composite liners that represent only an incremental improvement over traditional polymer and metallic liners.
There is accordingly a general need in the art for improved composite-lined and linerless, all-composite pressure vessel structures.